Various forms of suspension systems have been proposed and developed for bicycles. The most common form of fork suspension system for bicycles is comprised of suspension forks. These systems include two telescoping assemblies mounted to the front wheel of the bike. The telescoping assemblies include a large diameter tube and a small diameter tube that reciprocates within the large tube. Either of these tubes can be connected to the wheel, but it is usually the large tube. A top bracket bridges the telescoping assembly and the steering tube extends from the top bracket into the head tube. The maximum clearance for this type of system is the distance between the wheel and the top bracket. To increase clearance, the head tube must be raised.
Another type of suspension system commonly found on downhill bicycles is similar to that used on motorcycles and comprises a pair of telescoping assemblies between which the front wheel is mounted. Each telescoping assembly comprises an outer tube, and an inner tube which is free to move in and out of the outer tube and is cushioned in some manner. Generally, the outer tubes are connected at the lower ends to the axle of the front wheel of the bicycle, and the upper ends of the inner tubes are connected together by a pair of brackets that extend forwardly from the steering tube and head tube. These systems generally incorporate an oversized or large diameter axle to provide stiffness between the forks. Of course, such axles also require special hubs, which makes them use specific.
Other bicycle suspension arrangements comprise a single telescoping assembly in the head tube of the bike. In this type of suspension system, the front forks are formed by an integral blade. A inner tube extends from the blade into an outer tube that is mounted in the bike's head tube. This type of system provides a rigid blade system for more control, but the suspension travel is limited by the length and height of the head tube.
In all of these suspensions, bushings are usually provided between the telescoping tubes to reduce friction.
Riders have found that suspension front forks can benefit handling and improve control, and a front suspension helps the front wheel follow the ground. A front suspension system is desirable for absorbing bumps, and can enable the bicycle to handle better at higher speeds and be more controllable under rough conditions. The dual telescoping assembly presently used on some bicycles is essentially an adaptation of motorcycle front suspension technology; however, the two telescoping assemblies also have to be fixed together in some manner, as through a "U" shaped yoke at the upper ends of the tubes to eliminate the attendant twisting problem that occurs with each telescoping assembly. Moreover, the round inner tube and round outer tube that are generally used do not restrict rotational movement well. Also for increased stiffness, these systems generally require bulky forks. This problem does not occur with motorcycles because the suspension fork assembly can be large and bulky so as to overcome the twisting and independent leg motion problems. Additionally, there are linkage type systems, such as the aircraft landing gear scissors link, but this involves an additional coupling with its attendant weight, size and complexity.
Several prior art examples of front suspension systems for bicycles are shown in Horack U.S. Pat. No. 689,970 and Moulton U.S. Pat. No. 3,208,767. The Horack System provides a spring suspension, and includes a ball bearing system for allowing both an axial telescoping action and a rotary steering action. The Moulton patent discloses a spline-type spring suspension. Other suspension systems of interest are shown in Thoms U.S. Pat. No. 723,075, Hutchins U.S. Pat. No. 2,477,748, Ryan U.S. Pat. No. 3,301,575, Hornsby U.S. Pat. No. 3,459,441, Zenser U.S. Pat. No. 3,964,765, Hartman U.S. Pat. No. 4,815,763, Browning U.S. Pat. No. 5,308,099, British Specification No. 295316 of November 1928, and Italian Patent No. 416,260 of November 1946.
As is known to those skilled in the art, any form of system using anti-friction bushings and the like have undesirable static friction called "stiction." Because of this, suspension systems using such bushings tend to stick and then suddenly release or move, and the point at which they release gets higher with higher loads (eg, a higher radial load caused by a braking load).
It is desirable to provide a front suspension system or suspension fork for bicycles, and particularly for lightweight bicycles, which can bear a combination of loads comprising very high radial loads (e.g., from front to back) occasioned by braking, bumps and the like, while at the same time providing stable and tight rotational motion in steering of the front wheel through the suspension system from the handlebars. It is further desirable to provide a suspension system that provides maximum suspension travel.